The present invention concerns a device for securing a dial in a watchcase, or any other timepiece to enable the watch movement and the dial to be pre-assembled before mounting the other exterior watch parts. The invention concerns more particularly a device of this type in which the dial is secured to the casing ring.
A large number of devices have already been proposed for immobilising a dial on, or between, the constituent elements of a watchcase. Many devices concern clamping the dial between one or more lower elements, such as a plate, a casing ring or a middle part, and one, or more upper elements, such as a flange, a crystal or a bezel. These types of devices are well suited to manual assembly, but are less satisfactory for automatic or semi-automatic assembly, where pre-assembly of the movement, dial and display device is desirable before the exterior watch elements are assembled.
Several solutions have been proposed to achieve the above object. It is for example possible to screw the dial at two or three points on the bottom of the plate or on the casing ring. Japanese Patent Application No. 1467/96 proposes a bolt connection at the centre with a passage for the hand pipes. U.S. Pat. No. 4,320,483 discloses a magnetic coupling device between the dial and the plate.
Among the other solutions which have given rise to numerous variants, the principle consisting in providing feet secured to the lower surface of the dial should be cited, said feet being immobilised in a lower element of the case by welding, screwing or locking. As regards locking, European Patent No. 0 465 988 may be cited wherein each foot of the dial is locked into the plate by a post riveted in proximity thereto.
According to a simpler solution, disclosed in Swiss Patent No. 485 259, the dial feet are bonded inside housings arranged in the casing ring. One could even envisage an even simpler embodiment wherein the dial has no feet and wherein the bonding is done directly on the upper surface of the casing ring. All cases necessitate a product that can bond both the material of the dial and that of the casing ring, or of any other lower connecting element. This is most often the case, but it sometimes happens that it is impossible to find such a product in particular when the casing ring is a synthetic material for which no adhesive with sufficient adhesion currently exists.
The object of the present invention is thus to provide a simple and economic assembly of a dial with a lower element of a watchcase, in particular a casing ring, using an adhesive material.
The invention therefore concerns a device for securing a dial onto a lower element of a case intended to accommodate a watch movement, or onto a lower element contained therein. The device is characterised in that the lower element includes at least two through passages each having a first part on the dial side separated from a second part on the opposite side by a neck portion, the whole of their first part and at least a portion of the second part of said passages being filled with an adhesive material having a strong power of adhesion to at least the material forming the lower face of the dial.
As will be seen in the following detailed description, the neck portion may be obtained in different ways. In a preferred embodiment, the first and second parts of the through passages form paths with their generators perpendicular to the general plane of the case, i.e. to the dial itself. These paths evidently have a contour fitted to the space available for arranging the through passages through the lower element.
According to another embodiment, the axes of the first and second parts of the through passages form a broken line.
In order to facilitate pre-assembly of the dial to the movement, the lower element is preferably the casing ring or radial extensions of the bottom of the plate of the watch movement. The device according to the invention is particularly advantageous when the dial is secured onto casing ring. Indeed, one of the materials most commonly used to make casing rings is a polyoxymethylene, marketed by Duport under the trademark Delrin(copyright) because of its very low friction coefficient, which facilitates the assembly operations. Unfortunately, this material is excessively difficult, not to say impossible, to bond. The device according to the invention thus enables its tribological qualities to be used to advantage while allowing bonding with a dial, which does not require any particular conformation, such as feet to secure it.